The objectives of Project 2 are the refinement and application of G protein-dependent cell-based functional assays for monitoring Orexin 1 receptor (0X1R) activity, suitable to determine potency and mechanism of action of 0X1R antagonists that have the potential to be developed as novel therapeutics for the treatment of nicotine dependence. In addition, a series of G protein-independent cell-based functional assays will be developed and optimized to further characterize 0X1R ligands and allow for identification of compounds exhibiting 'functional selectivity'. Compounds synthesized in Project 1 and compounds emerging from the OXIR high throughput screening (HTS) campaign of the 'Molecular Libraries Probe Production Centers Network' (MLPCN) sample collection will be characterized in the aforementioned assays against recombinant 0X1R in high throughput fashion. Counterscreens to assess selectivity of high priority potent modulators will also be developed and activity of interesting compounds will be confirmed using primary neuronal cells to help bridge the gap between in vitro and in vivo pharmacology. This multiple assay approach together with pharmacokinetic data generated in Project 3 is designed to drive an iterative medicinal chemistry program (Project 1) aimed at identifying potent, selective, cell penetrant 0X1R antagonists that will advance to in vivo efficacy studies in animal models of nicotine dependence (Project 4).